Dave, I am far from an expert on zinc wicks but I've been doing some research and testing recently. Here's my opinion.... The zinc wicks will vary from suppliers...whether they get them from different facilities, they are coated in different wax's, or whatever I don't know, but I do know that some will perform differently than others. Not all of them of course, but I have gotten ones that didn't perform as well. The second number I believe has something to do with the speed that the fibers are woven together. hth, amanda